A Multiuse Nanopore Platform with Disposable Paper Analytical Device for the Detection of Heavy Meatal Ions

The pollution of heavy metal ions within the environmental is a global problem. The rapid and precise removal of these contaminants can be aided by identifying and quantifying the composition of the sample. It is therefore crucial to develop effective portable analytical techniques to determine the levels of heavy metal contamination. Paper-based analytical devices (PADs) offer a low cost method making them an excellent platform for onsite environmental sensors. Here we demonstrate how a PAD can be integrated into a multi-use Nanopore platform. The PAD was functionalised with different recognition ligands, who’s surface charge densities varied in the presence of an analyte. The surface of the PAD was placed in contact with a Nanopore which exhibited Ion Current Rectification (ICR). The extent of ICR, was dependent upon the PAD’s surface charge, and the presence of the analyte of interest i.e. the ICR phenomena was exaggerated or diminished indicating the presence of the metal ion in solution. We demonstrate the potential of PAD-ICR using a PAD functionalised with a peptide aptamer specific for nickel ions. Allowing the detection of nickel(II) as low as 0.25 μM even in the presence of other metal ions. After any measurement, the Nanopore surface can be wiped clean, and reused.

A Multiuse Nanopore Platform with Disposable Paper Analytical Device for the Detection of Heavy Meatal Ions

The pollution of heavy metal ions within the environmental is a global problem. The rapid and precise removal of these contaminants can be aided by identifying and quantifying the composition of the sample. It is therefore crucial to develop effective portable analytical techniques to determine the levels of heavy metal contamination. Paper-based analytical devices (PADs) offer a low cost method making them an excellent platform for onsite environmental sensors. Here we demonstrate how a PAD can be integrated into a multi-use Nanopore platform. The PAD was functionalised with different recognition ligands, who’s surface charge densities varied in the presence of an analyte. The surface of the PAD was placed in contact with a Nanopore which exhibited Ion Current Rectification (ICR). The extent of ICR, was dependent upon the PAD’s surface charge, and the presence of the analyte of interest i.e. the ICR phenomena was exaggerated or diminished indicating the presence of the metal ion in solution. We demonstrate the potential of PAD-ICR using a PAD functionalised with a peptide aptamer specific for nickel ions. Allowing the detection of nickel(II) as low as 0.25 μM even in the presence of other metal ions. After any measurement, the Nanopore surface can be wiped clean, and reused.

Ion Current Rectification in Extra-Long Nanofunnels

Nanofluidic systems offer new functionalities for the development of high sensitivity biosensors, but many of the interesting electrokinetic phenomena taking place inside or in the proximity of nanostructures are still not fully characterized. Here, to better understand the accumulation phenomena observed in fluidic systems with asymmetric nanostructures, we study the distribution of the ion concentration inside a long (more than 90 µm) micrometric funnel terminating with a nanochannel. We show numerical simulations, based on the finite element method, and analyze how the ion distribution changes depending on the average concentration of the working solutions. We also report on the effect of surface charge on the ion distribution inside a long funnel and analyze how the phenomena of ion current rectification depend on the applied voltage and on the working solution concentration. Our results can be used in the design and implementation of high-performance concentrators, which, if combined with high sensitivity detectors, could drive the development of a new class of miniaturized biosensors characterized by an improved sensitivity.

A Simulation Analysis of Nanofluidic Ion Current Rectification Using a Metal-Dielectric Janus Nanopore Driven by Induced-Charge Electrokinetic Phenomena

We propose herein a unique mechanism of generating tunable surface charges in a metal-dielectric Janus nanopore for the development of nanofluidic ion diode, wherein an uncharged metallic nanochannel is in serial connection with a dielectric nanopore of fixed surface charge. In response to an external electric field supplied by two probes located on both sides of the asymmetric Janus nanopore, the metallic portion of the nanochannel is electrochemically polarized, so that a critical junction is formed between regions with an enriched concentration of positive and negative ions in the bulk electrolyte adjacent to the conducting wall. The combined action of the field-induced bipolar induced double layer and the native unipolar double layer full of cations within the negatively-charged dielectric nanopore leads to a voltage-controllable heterogenous volumetric charge distribution. The electrochemical transport of field-induced counterions along the nanopore length direction creates an internal zone of ion enrichment/depletion, and thereby enhancement/suppression of the resulting electric current inside the Janus nanopore for reverse working status of the nanofluidic ion diode. A mathematical model based upon continuum mechanics is established to study the feasibility of the Janus nanochannel in causing sufficient ion current rectification, and we find that only a good matching between pore diameter and Debye length is able to result in a reliable rectifying functionality for practical applications. This rectification effect is reminiscent of the typical bipolar membrane, but much more flexible on account of the nature of a voltage-based control due to induced-charge electrokinetic polarization of the conducting end, which may hold promise for osmotic energy conversion wherein an electric current appears due to a difference in salt concentration. Our theoretical demonstration of a composite metal-dielectric ion-selective medium provides useful guidelines for construction of flexible on-chip platforms utilizing induced-charge electrokinetic phenomena for a high degree of freedom ion current control.